Combustion turbines are used both in an industrial capacity for generation of power, as a prime mover in certain applications such as locomotives, and in jet aircraft engines. At the present time, the control of the output of industrial/electric utility gas turbines is accomplished by measuring the turbine exhaust total temperature relative to the exhaust duct; and specifically this is done by, for example, thermocouples in the exhaust gas duct. Ideally the firing temperature in the combustion chamber should be directly measured but this is not possible because of the harsh conditions within the chamber. Thus, the firing temperature has to be inferred by using the thermocouples placed inside the exhaust duct outlet of the turbine.
A number of problems are associated with the above prior technique. For example, gases exiting the turbine are not always uniform in temperature at exhaust gas measuring points and therefore any derived average temperature is inaccurate.
Infrared thermometry has also been successfully employed in industrial gas turbines to monitor metal temperatures of the first turbine blade. This is then combined with the exhaust thermocouple average to provide some kind of measurement of gas bulk temperature. But still this method is not accurate especially since the first stage temperatures are quite variable due to blade cooling, and variation in coolant flow bypassing the first stage for cooling later rows, etc.